let _Vue=null

export default class VueRouter{
    static install (Vue){
        // 1.判断当前插件是否已经被安装
        if(VueRouter.install.installed){
            return
        }
        VueRouter.install.installed=true
        // 2.把vue构造函数记录到全局变量
        _Vue=Vue
        // 3.把创建vue实力时候传入的router对象注入到vue实力上
        _Vue.mixin({
            beforeCreate(){
                if(this.$options.router){
                    _Vue.prototype.$router=this.$options.router
                    this.$options.router.init()
                }
            }
        })
    }
    constructor(options){
        this.options=options
        this.routeMap={}
        this.data=_Vue.observable({
            current:'/'
        })
    }
    init(){
        this.createRouteMap()
        this.initComponents(_Vue)
        this.initEvent()
    }
    createRouteMap(){
        this.options.routes.forEach(route=>{
            this.routeMap[route.path]=route.component
        })
    }
    initComponents(Vue){
        Vue.component('router-link',{
            props:{
                to:String
            },
            render(h){
                return h('a',{
                    attrs:{
                        href:this.to
                    },
                    on:{
                        click:this.clickHandler
                    }
                },[this.$slots.default])
            },
            methods:{
                clickHandler(e){
                    history.pushState({},'',this.to) //添加历史
                    this.$router.data.current=this.to //加载组件
                    e.preventDefault()
                }
            }
            // template:'<a :href="to"><slot></slot></a>' //完整版vue
        })
        const self=this
        Vue.component('router-view',{
            render (h){
                const component = self.routeMap[self.data.current]
                return h(component)
            } 
        })
    }
    initEvent(){
        window.addEventListener('popstate',()=>{
            this.data.current=window.location.pathname
        })
    }
}